https://developers.weixin.qq.com/minigame/dev/api-backend/open-api/internet/internet.getUserEncryptKey.html

errcode: 87009,errmsg: "invalid signature rid: 63e0625b-46a40fb2-16bcd8bd"， 签名使用的是 hmac_sha256(session_key, "")

对应的golang代码是

func ComputeHmacSha256(message string, secret string) string { 
    key := []byte(secret)
    h := hmac.New(sha256.New, key)
    h.Write([]byte(message)) 
    sha := hex.EncodeToString(h.Sum(nil))  
    return base64.StdEncoding.EncodeToString([]byte(sha)) 
}